Human neural systems that mediate visual perception, attention, and memory were investigated in the intact brain with functional brain imaging. Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) were used to measure precisely localized hemodynamic changes associated with the performance of selected visual perceptual and mnemonic tasks. These hemodynamic changes are indices of local changes in neural activity. Human extrastriate visual cortex, like that of the macaque monkey, was found to be organized into a ventral object vision stream and a dorsal spatial vision stream. Cortical areas in the ventral object vision pathway demonstrated functional specialization with distinct areas associated with color perception as compared to the perception of faces and other objects. Different categories of objects, such as faces, houses, and chairs, differentially activate regions of ventral extrastriate cortex, suggesting that the neural representations of the features that define categories cluster together. Thus the representation of vision is converted from a retinotopic organization in early visual areas to an objectopic representation in later ventral extrastriate areas. The complete object and spatial visual processing streams, including posterior extrastriate and prefrontal projections, participate in object and spatial visual working memory. Different prefrontal areas were associated with object and spatial visual working memory. Spatial working memory activated a region in the superior frontal sulcus just anterior to the human frontal eye field. Three, anatomically and functionally distinct prefrontal regions in the middle and inferior frontal gyri were identified that participate in object working memory. - Visual Perception, Attention, Memory, PET, fMRI, - Human Subjects